Many internal combustion engines utilize cooperative engine cylinder and piston arrangements to generate power using a pumping motion. Engine cylinder and piston arrangements may be used to intake or scavenge an air-fuel mixture or strictly air charge (in fuel injected engines) for combustion and expel spent exhaust gases in multicycle operations, such as, for example, in 2-cycle and 4-cycle operations. While embodiments of the present invention have primary use for 4-cycle engine operation, the claims defining the invention are not limited to 4-cycle engines unless such limitation is expressly set forth in the claims.
Further, it is to be appreciated that the reference herein to an engine “cylinder” is not limited to a combustion chamber having a cylindrical shape or circular cross-section. Instead, the term cylinder refers to any combustion chamber or cavity of any shape that receives a piston having an outer shape adapted to effectively seal (i.e., to permit an acceptable level of leakage) with the sidewall of the cylinder. The seal should be in effect as the piston slides back and forth reciprocally within the engine cylinder in a pumping motion.
Engine cylinders may include one or more intake ports and one or more exhaust ports that, collectively, permit gases to flow into, and out of, the engine cylinder, respectively. Engine valves, such as poppet valves, may be used to selectively open and close the intake and exhaust ports. The selectively timed opening and closing of the intake and exhaust valves, in conjunction with the pumping motion of the engine pistons and the introduction of fuel, may provide an air/fuel charge to the engine cylinder for combustion and removal of the spent charge exhaust gases from the cylinder after combustion.
Existing internal combustion engine pistons used for Otto cycle or Diesel cycle operation, for example, typically have a generally cylindrical shape. More specifically, the typical Otto or Diesel cycle engine piston may have a generally smooth cylindrically shaped skirt with a circular cross-section that includes circumferential recesses to receive one or more sealing piston rings. The piston and piston ring assembly may slide reciprocally within a cylinder between top dead center and bottom dead center positions. The interface of the piston rings with the cylinder wall may be lubricated with engine oil, for example.
The efficiency of a particular engine design may be a function of many factors. Among others, these factors include engine weight to power ratio, as well as the overhead space available for the placement of intake valves, exhaust valves, auxiliary valves, spark plugs, glow plugs, fuel injectors and water injectors. Engine power is often a function, at least in part, of cylinder displacement. Engine weight is a function, at least in part, of the space required to house the engine pistons, which is a function of the engine cylinder and piston shape. Cylindrically shaped engine pistons require a certain amount of space per unit volume of displacement, and the required space is a function of the diameter of the piston skirt. The overhead space available for the placement of intake valves, exhaust valves, auxiliary valves, spark plugs, glow plugs, fuel injectors and water injectors in cylindrically shaped engine pistons is also limited by (i.e., a function of) the diameter of the piston skirt. Accordingly, circular cross-section engine cylinders and pistons may be less desirable in terms of engine space, weight and overhead space, than non-circular cross-section pistons and cylinders, for a given engine displacement and power rating.
Honda developed one known example of a non-circular cross-section engine piston for a motorcycle engine. Honda's oval piston internal combustion engine is described in U.S. Pat. No. 4,383,508 to Irimajiri et al. Honda employed oval pistons to obtain increased cylinder displacement and increased overhead area available for valves, spark plugs, and injectors. However, Honda's oval shaped piston engine was not optimal, and required the use of two connecting rods between each piston and the crankshaft, thereby increasing the weight and size of the overall engine. The Honda oval pistons also required the use of special technology to keep the pistons moving parallel to the cylinder block walls, thereby increasing weight and complexity of the engine. Accordingly, there is a need for engines with non-circular cross-section cylinders and pistons that improve upon the Honda implementation in terms of weight, space required, and the placement of intake valves, exhaust valves, auxiliary valves, spark plugs, glow plugs, fuel injectors and water injectors.
Two additional factors which impact engine efficiency are flame front propagation during combustion of fuel, and effective force transfer from the expansion of combustion gases to the piston used to generate power. Pistons having an upper end or head with a hemispherical or domed shape are known for their efficient flame front propagation properties and effective force transfer of combustion gases to piston. However, hemispherical pistons were not utilized in engines with non-circular cross-section cylinders and pistons. Accordingly, there is a need for pistons with hemispherical or domed heads to be used in engines with non-circular cross-section cylinders and pistons.
Engine space and weight is also a function of crankshaft and connector rod design. As already noted, the Honda engine employing particular oval cross-section pistons required two connector rods per piston, thereby increasing engine weight and complexity. Accordingly, there is a need for compact crankshaft and connector rod assemblies for use with non-circular cross-section pistons in particular, and for all engines generally, that is optimal in terms of weight, required space, cost, and/or reliability.
The manufacturing cost and the repair cost are also factors that require consideration for commercialization of the engines. Crankshaft assemblies typically require the use of splined elements to join the constituent elements, such as shafts, and cranks, together. Splined elements may require relatively expensive manufacturing processes to produce, and are relatively difficult and expensive to repair. Moreover, it is desirable for some engines to permit the center shaft of a crankshaft assembly to break away cleanly from the other elements to which it is connected during an engine failure condition. Crankshaft elements joined using splines are not well suited to break away from each other during an engine failure, and if they were designed to do so, repair would likely be difficult and expensive. Accordingly, there is a need for crankshaft assemblies that do not require splined elements to join the constituent parts of the assemblies together.
Internal combustion engines almost universally require liquid lubricant, such as engine oil, to lubricate the interface between the piston and the cylinder within which it moves back and forth in a reciprocal motion. Lubrication systems are usually mission critical and the failure of a lubrication system can be catastrophic. The need for a piston lubricant brings with it many disadvantages. The lubricant wears out and becomes contaminated over time, and thus requires replacement, adding expense and inconvenience to engine operation. Many lubricants require pumps and passages to reapply the lubricant to moving parts, such as the engine pistons. Pumps and passages, and other elements of an active lubrication system need to operate correctly and require seals between interconnected elements. Lubrication system leaks naturally occur as seals deteriorate over time, and pumps leak and wear out, adding still further maintenance expense and inconvenience to engine operation. Leaks can also permit lubricant to enter the combustion chamber, interfering with combustion, and fouling injectors and spark or glow plugs. Lubricant in the combustion chamber can also result in unwanted exhaust emissions. Leaks can also result in the contamination of the lubricant with combustion by-products. All of the foregoing issues are attendant to the use of lubricated pistons, and all add failure modes and maintenance costs. Accordingly, there is a need for internal combustion engines that depend less, or not at all, on piston lubrication.
Engine efficiency and power may also be a function of the mass of air in the combustion chamber. The air mass that can be loaded into the combustion chamber is a function of the pressure differential between the combustion chamber and the intake air source (e.g., manifold) during the intake cycle, as well as the effective size and flow characteristics of the intake port, and the duration of the intake cycle event. Increasing any one or more of the intake air pressure, the effective size and/or flow profile of the intake port, and/or the effective intake cycle duration, will tend to increase air mass in the combustion chamber, and thus improve efficiency and power. Accordingly, there is a need for engines and methods of engine operation that increase and/or improve intake air pressure, intake port size and flow, and/or intake event duration.
In addition to improving air mass transfer to the engine cylinder for combustion, improved engine efficiency and power may also result from optimal swirl and turbulence of the intake air or air/fuel mixtures in cylinder squish areas. The swirl and turbulence produced in squish areas is a function of numerous factors, including the shape of the upper end of the piston and cylinder head defining the combustion chamber. Accordingly, there is a need for engine pistons and cylinders shaped to promote optimal swirl and turbulence in the combustion chamber squish areas.
Engine efficiency and power, resulting from air mass transfer to the engine cylinder for combustion for example, may also be a function of the timing of the opening and closing of engine intake valves. The timing for opening and closing exhaust and auxiliary valves can also affect efficiency and power. Conventional fixed time valve actuation may be set to be optimal for one set of engine operation parameters (e.g., ambient temperature, pressure, fuel type and richness of mixture, engine speed and load, etc.). Fixed time valve actuation may be sub-optimal for all other combinations of engine operation conditions. In order to provide improved efficiency and power, engines have been provided with variable valve actuators (VVA), however the control of existing VVA systems may be complicated and expensive. Accordingly, there is a need for intake, exhaust, and auxiliary variable valve actuation systems that provide variable valve timing without the need for overly complicated or expensive componentry.
Some vehicles and other engine powered machines may benefit from engines having a low center of mass relative to the vehicle or machine structure. A low center of mass may improve handling characteristics, for example. Known internal combustion engines have centers of mass dictated, at least in part, by the need to place heavy cylinder heads and associated components at the top of the engines. The location of the cylinder heads at the top of the engines results from the need to lubricate the pistons in a manner that restricts the amount of lubricating oil that enters the combustion chambers. Accordingly, there is a need for engines with innovative piston lubrication solutions. New lubrication systems, methods and/or substitutes may eliminate the need to place heavy cylinder heads and associated components at the top of the engine thereby permitting the design of engines with a lower center of mass compared to other engines of comparable weight, power and cost.